The present invention relates generally to a method and apparatus for forming a metal plate. More specifically, the present invention relates to a method and apparatus for cutting and perforating a metal plate optionally accompanied by forming the plate into a three-dimensional (3-D) shape.
Metal plates of various sizes and thickness are a starting material for the preparation of a variety of objects. Metal plates can be shaped to assume a 3-D shape, may be cut, perforated, etc. Cutting and perforation are achieved in the art by the use of presses, by the use of a laser, etc.
The invention, has at its object to provide a novel cutting and perforation method.
The present invention is based on the realization and observation that a metal plate which is intensely forced against a surface with boundaries or openings defined by wall sections essentially normal to the plate and thus parallel to the direction of application of the force is cut along lines defmed by said wall sections. In other words, the point of intersection of said wall sections and said surface defines a shearing line and acts as a knife in such a process. Thus, in accordance with the present invention a metal plate is forced against a mold formed with such edges or openings, whereby edge portions (portions defined between a cut line and the edge of the plate) may be cut away and openings (or perforations) formed within the plate. The force, by one embodiment, may be a pulsed magnetic force. In accordance with another embodiment, the force may be that generated by a shock wave generated in a fluid.
The present invention thus provides a method for forming a metal plate, comprising:
(a) providing a mold with a forming plane which in operation faces the plate, having at least one of openings or boundaries defined by wall sections extending essentially normal to said forming plane, edges of said openings or boundaries defining shearing lines;
(b) placing the plate against said forming plane; and
(c) generating an abrupt and intense pressure pulse and applying it onto said plate to force it towards said mold, whereby said plate is cut along said cut lines.
The present invention also provides an apparatus for forming a metal plate, comprising:
(i) a mold comprising a forming plane which in operation faces the plate, having at least one of openings or boundaries defined by wall sections extending essentially normal to said forming plane, said openings or boundaries defining cut lines; and
(ii) a device for generating an abrupt and intense force pulse and for applying it onto said plate to force it towards said mold, to cut said plate along said cut lines.
In accordance with one embodiment of the invention, said force pulse is a pulsed magnetic force (PMF). The PMF may be generated by a PMF device comprising one or more forming coils, which are typically concentric, placed opposite and proximal to the forming plane and extending peripheral to its boundaries. Each forming coil is connected to an electric discharge circuitry for discharging a short and intense electric current pulse through the forming coil to yield the PMF to form said metal plate.
A background on prior art apparatuses and methods for working of metal workpieces by the PMF process can be found in U.S. Pat. Nos. 3,654,787, 3,961,739, 4,170,887, 4,531,393, 4,807,731, 5,353,617 and 5,442,846, and in PCT Application Publication No. WO 97/22426.
In accordance with another embodiment of the invention, the force pulse is a result of a pressure pulse generated by the breakdown or discharge of an intense electric current through a fluid of a discharge-in-fluid (DIF) device. A DIF device comprises a fluid basin and of electric discharge electrodes embedded within the fluid, which are connected to an electric discharge circuitry for discharging a short and intense electric current within the fluid. The discharge generates an electric spark or breakdown within the fluid which yields the formation of plasma, vapor or both and consequently a pressure wave. The fluid basin has an opening, which may at times be sealed by a flexible membrane, which opening is close proximity, usually in contact with the plate. Thus, the abrupt pressure wave generated within the DIF device is thereby transmitted to the plate. The fluid in the basin is preferably a liquid, particularly an aqueous solution.
In accordance with vet another embodiment, the force pulse is a combined PMF and a DIF generated force. For example, the actual portion of the plate may be formed by a DIF device, while peripheral portions with a PMF; through a forming coil disposed peripheral to a DIF device.
An abrupt and intense pressure may also be achieved by other means such as, for example, by means of an explosive charge.
Where the mold comprises openings, holes will form in the plate at locations corresponding to the openings. For example, where the plate is intended to be used as a satellite dish, such openings may be used as through holes for passing screws through the plate to fasten them to a support structure.
Where the mold comprises said boundaries, edge portions of the plate are cut off along lines defined by said boundaries, with the cut boundaries then defining edges of the formed plates.
As will no doubt be appreciated, at times, a plate may be simultaneously cut along boundaries as well as perforated with holes. Furthermore, typically, the plate is simultaneously shaped to assume a 3-D shape defined by a mold""s contours and simultaneously cut along its edges and perforated.
In the case of a satellite dish, it is at times desired (particularly for structure reinforcement) to form a dish with a downward depending peripheral skirt portion relative to its front plane. This requires first bending of its peripheral edge portions and then trimming the bent edge portions so that the skirt will have a desired width. This feat is very difficult to attain in accordance with the prior art. The invention also provides a method and apparatus for the formation of a dish with such a peripheral skirt. A method for forming a metal plate with a depending peripheral skirt portion, in accordance with this aspect, comprises:
(a) providing a mold having an overall annular shape and a forming plane, which in operation faces the plate, having rounded edges;
(b) placing the plate against said forming plane; and
(c) generating an abrupt and intense force pulse and applying it onto said plate to force it towards said mold, whereby said plate is formed to assume a 3-D shape corresponding to contours of the mold, while edge portions with edge portions of the plate being bent about said rounded edges; and
(d) applying a pulse magnetic force (PMF) onto said edge portion in a direction which is essentially normal to said edge portion against a shearing line defined between a face having said edge portion and a wall portion normal thereto, whereby said edge portion is cut along said shearing line.
This aspect also provides an apparatus for forming a metal plate, comprising:
(i) a mold with a forming plane which in operation faces the plate, having rounded edges;
(ii) a device for generating an abrupt and intense force pulse in an axis essentially normal to said forming plane and for applying it onto said plate to force it towards said mold and to force edged portions of the plate to bend about said rounded edges; and
(iii) an auxiliary pulsed magnetic force (PMF) device with an auxiliary forming coil for applying a PMF pulse onto and in a direction essentially normal to the bent edge portion of the plate against an edge portion retaining surface provided with shearing lines defined between said surface and wall portions perpendicular thereto; in an edge-shearing state of the operation the bent edge portion is retained between said surface and said auxiliary forming coil with said shearing line being opposite said auxiliary forming coil, whereby upon discharge of current through said auxiliary forming coil, said edge portion is cut along said shearing lines.
In accordance with one embodiment of the apparatus according to this last aspect, the forming coil is associated with the mold, e.g. placed in a recess in an annular side wall thereof and the shearing line is defined in an annular member which in said edge-trimming operational state is placed opposite said auxiliary forming coil. In accordance with another embodiment, said shearing line is defined in side wall of the mold and the forming coil is received within an edge-trimming operational state is placed opposite said shearing lines.
Said device for generating the intense force pulse may, in accordance with one embodiment, be a PMF device with a forming coil or may be a DIF device.
The present invention is applicable to forming metal plates of different shapes, of different metals, of different thickness, etc. As will be appreciated, the present invention is not limited to plates of any specific specification. The invention may be applied to large plates, to form relatively large objects, e.g. a satellite dish, and may also be applied for forming small components. At times, a mold used may in fact comprise a plurality of sub-mold structures, each defined by boundaries for the simultaneous preparation of a number of different objects from a single plate. In addition, although the present invention is defined with reference to the formation of a plate, it should be understood that at times the object of the process may be the cut-off portions themselves, e.g. portions defined by said openings or the trimmed peripheral edge portions. Thus, for example, openings of a desired shape may be used to define the shape of planar objects which are thus cut-off from the plate by the process of the invention.
In the following, the invention will be described in a non-limiting manner with reference to the annexed drawings.